1. Field of the Invention
The present invention relates to a video system and, more particularly, to a system for combining a predetermined image with an arbitrary image.
2. Description of the Related Art
It is known that a conventional device of this kind is arranged to superimpose an image such as a character, a symbol or a graphic image on an image which is being recorded as a video signal during photography using a video camera, in order to record information such as the date, time and place of the photography or to enhance image effects. A large number of such superimposing techniques have heretofore been known.
For example, a system utilizing what is called a character generator is widely used. The character generator typically comprises a pattern ROM (read-only memory) in which display patterns such as characters and symbols are stored, a register which stores the kind of character to be displayed at each display position, and a reading part for reading the contents of the pattern ROM corresponding to the contents of the register in accordance with horizontal and vertical synchronizing signals and combining the read contents with a video signal. A microcomputer or the like writes the kind of character to be displayed to a register present at a desired display position, whereby the desired character is displayed.
A second example is a system which quantizes an imaged signal by an A/D converter by using a code of the order of one to several bits and stores a quantized signal in a memory for each display pixel. When a display operation is to be performed, the contents of the memory are sequentially read in accordance with the horizontal and vertical synchronizing signals of the imaged signals, and combined with a video signal.
A third example is a system which comprises a graphics memory corresponding to each display pixel in a picture, a microcomputer for writing display data to the graphics memory, and a reading circuit for reading the contents of the graphics memory. The microcomputer writes the display data to the graphics memory in accordance with a program, and the reading circuit reads the written data in accordance with horizontal and vertical synchronizing signals. The read signal is combined with a video signal.
However, each of the conventional examples described above has the following disadvantage.
In the system utilizing the character generator, the kinds and sizes of display characters and display symbols and the position where they can be displayed are limited. This system, therefore, has practical limitations in that it is only utilized for recording the abovedescribed specific kinds of information.
In the second example, since image data on each pixel is stored in a memory, the body of the system requires a large-capacity memory, and a character or graphic image to be displayed needs to be drawn on paper or the like in advance. This system still has practical limitations in that it is impossible to always perform image combination by an easy operation.
In the third example, a graphics memory is needed for each pixel, so that the required memory capacity is extremely large. Since an image is drawn on the graphics memories by the microcomputer, a high-performance microcomputer is needed.
If a moving image is displayed, the first example will encounter the problem that the displayed image can only be moved within a limited range, and the second example will encounter the problem that the displayed image is difficult to move partially, i.e., it can only be scrolled. In the case of the third example, since the number of times of computations by the microcomputer is enormous, a microcomputer capable of performing higher-speed computations is needed.